An image can be represented by means of an appropriate image representation device. For example, an image can be displayed by a display device comprising a display screen or other means for presenting an image based on image data. The image data can be created, for example, by means of a digital camera. When a photograph is taken by the digital camera, the digital camera creates an image data file that may be stored in a memory means of the camera. The image data may also or alternatively be stored in a removable data carrier, such as in a tape, CD (compact disc) or a memory card. Digital cameras are well known in the art, and will thus not be explained in more detail herein.
Typically the image or audio data is stored in a file, record or similar data unit. It is possible to compress the data stored in the data unit. The compressed data requires less storage capacity when stored in an appropriate data storage means. A reason for the compression is that the digital cameras or other portable devices are typically provided only with a limited storage capacity. Furthermore, if the data unit is to be transported between two or more devices, compressed data files require less transportation capacity from the communication media between the devices.
An example of compressed data units is a compressed JPEG file for storing image data. The term ‘JPEG’ stands for Joint Photographic Experts Group which is formed by experts nominated by standards bodies and major companies. A standard by the JPEG is IS 10918-1 (ITU-T T.81), which is the first of a multi-part set of standards for still image compression. JPEG is based on the features of this standard, in association with a JFIF file format by C-Cube Microsystems.
Digital cameras typically compress images with a so called lossy compress algorithm before storing these to a memory. The above referenced JPEG supports the lossy compression. By means of the lossy compression the size of the image files can be made small enough so that it is possible to store the image data in limited storage capacity of the camera. A disadvantage of the lossy compression technique is that it loses information during the compressing operations.
One important feature of the digital photography is that it is possible to adjust and edit the images afterwards. The changes can be made by anybody. That is, the creator (i.e. the photographer) or the viewer or any other person in a chain between the creator and the viewer may edit or otherwise alter the image.
A possible editing task is the so called image cropping. In the image cropping unnecessary or otherwise unwanted areas of the image are cut out from the boundary areas of the image. In that way image size resolution, and thus size of the image file can be reduced.
An unwanted side effect of the editing processes is that the quality of the image may be reduced. For example, if an image is cropped and stored successive times the quality of image may be reduced in each editing cycle comprising decompression-compression and storing. This is caused by the possibility of loosing information during the image compression stages, especially if a lossy compression algorithm is used.
Thus the quality of the image may be reduced every time the image is fetched from, decompressed, compressed and stored again in the image data file. Since this cycle may happen every time the image data is processed, the quality of the image may get progressively worse each time an image is subjected to modifications.
The above discusses storing of the images in a lossy compression format. Another possibility is to store images by so called lossless compression formats. JPEG2000 is an example of a compression standard supporting both lossy and lossless compression. However, the lossless formats require more memory capacity for the image data storing than the lossy formats. Therefore the lossless formats may not be suitable for substantially small portable devices, such as for example digital cameras or display devices.
Digital imaging is gaining more popularity. An especially rapidly growing area of digital image handling is believed to be transportation of digital image data over data networks. At least the transmitting device or the receiving device may be a portable user equipment or other mobile station capable of communication over a wireless interface with the data network apparatus. As the size and/or weight is typically an important feature of the portable devices, the above discussed limitations in size and memory capacity need to be taken into consideration when designing such devices.
The end users of the image capturing or displaying devices may also wish to be more readily able to define the borderlines of an image. To enable this it is likely that even the user equipment will be provided with at least some level of borderline adjustment facility. The inventor believes also that at least in the first wireless image data transmission devices the image compression methods are likely to be based on lossy compression techniques. This is believed to be so because of the pixel count in the image and demands on storing capacity grow faster than technologies that may be used to increase the storage capacity. However, the deteriorating quality of the images may become a problem also with devices that are based on the lossless techniques.